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71.
We report current-induced magnetization reversal in a ferromagnetic semiconductor-based magnetic tunnel junction (Ga,Mn)As/AlAs/(Ga,Mn)As prepared by molecular beam epitaxy on a p-GaAs(001) substrate. A change in magneto-resistance that is asymmetric with respect to the current direction is found with the excitation current of 106 A/cm2. Contributions of both unpolarized and spin-polarized components are examined, and we conclude that the partial magnetization reversal occurs in the (Ga,Mn)As layer having smaller magnetization with the spin-polarized tunneling current of 105 A/cm2. 相似文献
72.
根据轴线地质剖面和隧道轴线布置图,对某拟建中水下公路隧道最小安全顶板厚度的确定进行了研究,通过比较得出最合理的最小安全顶板厚度,对同类工程有很大的参考价值。 相似文献
73.
Ralf KretzschmarAuthor VitaeNicolaos B. KarayiannisAuthor Vitae Hans RichnerAuthor Vitae 《Pattern recognition》2003,36(11):2699-2712
This paper presents the results of a study that relied on trainable neural network classifiers to identify and remove bird-contaminated data from wind measurements recorded by a 1290-MHz wind profiler. A wind profiler is a Doppler radar system measuring the three-dimensional wind field. Migrating birds crossing the radar beam can lead to erroneous wind observations. Bird removal was performed by training conventional feedforward neural networks (FFNNs) and quantum neural networks (QNNs) to identify and remove bird-contaminated data recorded by a 1290-MHz wind profiler. A series of experiments evaluated several sets of input features extracted from wind profiler data, various FFNNs and QNNs of different sizes, and criteria employed for identifying birds in wind profiler data. 相似文献
74.
一种多变量自校正前馈解耦PID控制器及其应用 总被引:2,自引:0,他引:2
提出一种多变量自校正前馈解耦PID控制器。利用UJury法确定了对任意时延,使闭环系统稳定的条件。 相似文献
75.
隧道窑由于燃用重油造成生产成本升高,为此探讨采用煤焦油沥青配制的燃料油替代重油燃烧。通过调节燃料油的温度和加入蒽油的比例解决了其粘度过大造成燃烧不完全的问题;同时改进烧嘴结构,使雾化效果更好,燃烧更加完全。试验证明,隧道窑燃用燃料油经济可行。 相似文献
76.
K. D. Pham G. Jin M. K. Sain B. F. Spencer Jr. S. R. Liberty 《Canadian Metallurgical Quarterly》2004,130(4):466-470
This paper presents a comprehensive study of the stage-3 benchmark problem for response control of wind-excited tall buildings based on the linear quadratic gaussian (LQG) approach, and on its generalization, the k-cost-cumulant control method. For control design, the original nodal building model is first transformed into balanced modal space. The Hankel singular values (HSVs) and the power spectral density of the wind disturbances are calculated; and, based on them, a reduced-order model is derived by keeping the first six low-frequency modes. A balanced LQG (BLQG) controller is then determined by adopting the HSVs as a basis to choose the design weights. The main results of the paper are that the BLQG control design is able to come within 5–10% of the performance of the sample LQG controller supplied with the benchmark, but with control actions on the order of one-third less than the sample LQG, and with stability improvement features of a substantial nature over the range of stiffness perturbations specified in the benchmark. Finally, if the low authority BLQG controller is regarded as a one-cost-cumulant design, then with the appropriate use of the second-cost cumulant, the latter methodology is able to demonstrate how higher-authority controllers can give certain improvements in performance, but at the expense of significant investment in control action. 相似文献
77.
Ho-Kyung Kim Masanobu Shinozuka Sung-Pil Chang 《Canadian Metallurgical Quarterly》2004,130(7):848-857
A geometrically nonlinear buffeting analysis of a cable-stayed bridge in the time domain is described. The bridge structure is modeled with three-dimensional thin-walled beam elements and three-dimensional elastic catenary cable elements. Spatially correlated wind velocity fluctuations are modeled and simulated using an algorithm for generating sample functions of a stationary, multivariate stochastic process according to its prescribed cross-spectral density matrix. Aerodynamic damping and aerodynamic stiffness are formulated based on experimentally determined flutter derivatives. The focus of this paper is on the effect of fluctuating components of the spatially correlated wind velocity on the geometrically nonlinear buffeting response for an 870 m cable-stayed bridge. 相似文献
78.
79.
Extreme winds, hurricanes, and tornadoes produce significant damage to electrical transmission and distribution line structures. The damage produces loss of power to the affected communities for a variable length of time, depending on severity of damage. Most institutions whose operations would be life threatening in the event of power failure have emergency power. However, loss of power to both residences and businesses can have economic impact on the community in the form of temporary housing shortages and loss of business. Utility companies seem to cope with wind damage fairly well, following risk management procedures in designing for wind and in providing alternate routing for distribution lines. However, continuing research and developments are needed to keep abreast of the problem. 相似文献
80.
3D techniques are increasingly used in aerospace industry to improve quality and performance of aircrafts. This paper presents a 3D imaging technique for studying the aerodynamic shape and flight performance of micro air vehicles. 3D stereoscopic vision, based upon stroboscopic imaging, was utilized to obtain the 3D information of the aircraft's flexible aerodynamic surface. The aircraft models with deformable aerodynamic shape were designed and tested in a purpose-built wind tunnel experimental environment. After calculation of SIFT feature points and subdivision of triangular meshes, deformable surface of the aircraft's aerodynamic shape was represented. The aircraft's 3D visualization was used for analyzing unsteady deformation in the aerodynamic shape under external airflow disturbances. The results, together with aerodynamic forces measured in the experiment, will be useful to improve the flight performance and disturbance resistance ability of micro air vehicles. 相似文献